Image capturing apparatus and distance measuring method

ABSTRACT

An image capturing apparatus for obtaining information regarding a depth of a subject includes: an illumination unit operable to cast a first illumination light beam that mainly contains a first wavelength and has a first intensity distribution on a plane perpendicular to an optical axis of the first illumination light beam and a second illumination light beam mainly containing a second wavelength and a third wavelength and having a second intensity distribution on a plane perpendicular to an optical axis of the second illumination light beam onto the subject, the second and third wavelengths being different from the first wavelength, the second intensity distribution being different from the first intensity distribution; and a depth calculation unit operable to calculate a depth-direction distance to the subject based on outgoing light beams from the subject.

This patent application claims priority based on a Japanese patentapplication No. 2000-176142 filed on Jun. 12, 2000, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image capturing apparatus and adistance measuring method for obtaining information regarding adepth-direction distance to a subject. More particularly, the presentinvention relates to an image capturing apparatus and a distancemeasuring method for obtaining the information regarding a depth of thesubject by capturing outgoing light beams from the subject that isilluminated with light.

2. Description of the Related Art

As a method for obtaining information regarding a distance to an objector information regarding a position of the object, a three-dimensionalimage measuring method is known in which light having a pattern of, forexample, a slit or a stripe, is cast onto the object and the patterncast onto the object is captured and analyzed. There are a slit-lightprojection method (light cutting method) and a coded-pattern lightprojection method as typical measuring methods, which are described indetail in “Three-dimensional image measurement”by Seiji Inokuchi andKosuke Sato (Shokodo Co., Ltd.).

Japanese Patent Application Laying-Open No. 61-155909 (published onJul., 15, 1986) and Japanese Patent Application Laying-Open No.63-233312 (published on Sep. 29, 1988) disclose a distance measuringapparatus and a distance measuring method in which light beams are castonto a subject from different light-source positions and the distance tothe subject is measured based on the intensity ratio of the reflectedlight beams from the subject.

Japanese Patent Application Laying-Open No. 62-46207 (published on Feb.28, 1987) discloses a distance detecting apparatus that casts two lightbeams having different phases onto the subject and measures the distanceto the subject based on the phase difference between the light beamsreflected from the subject.

Moreover, “Development of Axi-Vision Camera”, Kawakita et al., 3D Imageconference '99, 1999, discloses a method for measuring the distance tothe subject in which the subject that is illuminated with light havingthe intensity modulated at a very high speed is captured by a camerahaving a high-speed shutter function, and the distance to the subject ismeasured from the degree of the intensity modulation that variesdepending on the distance to the subject.

Japanese Patent Application Laying-Open Nos. 10-48336 and 11-94520disclose an actual time-range finder that calculates the distance to thesubject by casting different light patterns having different wavelengthcharacteristics onto the subject and extracting wavelength components oflight reflected from the subject incident light.

In the conventional distance measuring apparatus and method, the timedifference occurs in the measurement because it is necessary tosuccessively cast the light from the different emission positions so asto measure the reflected light beams, as disclosed in Japanese PatentApplications Laying-Open Nos. 61-155909 and 63-233312. Thus, in a caseof the moving subject, the distance cannot be measured. In addition,during a time period in which the position of the light source ischanged to change the emission position, the measurement error may occurbecause of waver of the capturing apparatus.

Moreover, in a case of using light beams having different wavelengthcharacteristics, the light beams can be emitted simultaneously, and thereflected light beams can be separated by a filter prepared inaccordance with the wavelength characteristics of the light beams, sothat the intensities of the reflected light beams can be measured.However, if the spectral reflectance of the subject varies depending onthe wavelength, the intensities of the reflected light beams are alsodifferent depending on the wavelength thereof. The difference of thereflected-light intensities between the wavelengths may cause an errorwhen the depth-direction distance is calculated from the ratio of theintensities of the reflected light beams, thereby preventing the precisecalculation of the depth-direction distance.

The actual time-range finder disclosed in Japanese Patent ApplicationsLaying-Open Nos. 10-48336 and 11-94520 also uses the light havingdifferent wavelength characteristics for calculating the distance to thesubject. In a case where spectral reflectance is varied depending on aposition of the illuminated portion of the subject, however, the errormay be caused, thus preventing the precise calculation of thedepth-direction distance.

The distance measuring apparatus disclosed in Japanese PatentApplication Laying-Open No. 62-46207 requires a high-precision phasedetector for detecting the phase difference. This makes the apparatusexpensive and loses the simplicity of the apparatus. In addition, sincethis apparatus measures the phase of the reflected light beam from apoint of the subject, it cannot measure the depth distribution of thewhole subject.

Moreover, in the distance measuring method using the intensitymodulation disclosed in “Development Axi-Vision Camera” by Kawakita etal. (3D Image Conference '99, 1999), it is necessary to perform thelight modulation at a very high speed in order to realize theintensity-modulation. Thus, a simple measurement cannot be realized. Inaddition, the measurement may include the time difference, thuspreventing a precise measurement for the moving subject.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide an imagecapturing apparatus and a distance measuring method that overcome theabove issues in the related art. This object is achieved by combinationsdescribed in the independent claims. The dependent claims define furtheradvantageous and exemplary combinations of the present invention.

According to the first aspect of the present invention, an imagecapturing apparatus for obtaining information regarding a depth of asubject, comprises: an illumination unit operable to cast a firstillumination light beam mainly containing a first wavelength and havinga first intensity distribution on a plane perpendicular to an opticalaxis of the first illumination light beam and a second illuminationlight beam mainly containing a second wavelength and a third wavelengthand having a second intensity distribution on a plane perpendicular toan optical axis of the second illumination light beam onto the subject,the second and third wavelengths being different from the firstwavelength, the second intensity distribution being different from thefirst intensity distribution; and a depth calculation unit operable tocalculate a depth-direction distance to the subject based on outgoinglight beams from the subject.

The first illumination light beam may have an intensity thatmonotonously increases along a first direction on the planeperpendicular to the optical axis thereof, and the second illuminationlight beam may have an intensity that monotonously decreases along asecond direction on the plane perpendicular to the optical axis thereof,the second direction being opposite to the first direction.

The first illumination light beam may have the first intensitydistribution in which, with increase of a distance from the optical axisthereof on the plane perpendicular to the optical axis, an intensitymonotonously increases or decreases, and the second illumination lightmay have the second intensity distribution in which, with increase of adistance from the optical axis thereof on the plane perpendicular to theoptical axis, an intensity monotonously decreases when the firstillumination light increases or increases when the first illuminationlight decreases.

The illumination unit may cast the first and second illumination lightbeams onto the subject simultaneously.

The image capturing apparatus may further comprise: an opticallyconverging unit operable to converge the outgoing light beams from thesubject onto which the first and second illumination light beams arecast; a separation unit operable to optically separate the outgoinglight beams into a first outgoing light beam having the firstwavelength, a second outgoing light beam having the second wavelength,and a third outgoing light beam having the third wavelength; alight-receiving unit operable to receive the first, second and thirdoutgoing light beams after being are separated by the separation unitand converged by the optically converging unit; and a light intensitydetector operable to detect intensities of the first, second and thirdoutgoing light beams received by the light-receiving unit, wherein thedepth calculation unit calculates the depth-direction distance to thesubject by using the intensities of the first, second and third outgoinglight beams.

The first illumination light beam may have an intensity that increaseson the plane perpendicular to the optical axis thereof along a firstdirection parallel to a line obtained by projecting a line connectingthe illumination unit to the light-receiving unit or the opticalconverging unit on the plane perpendicular to the optical axis thereof,and the second illumination light beam may have an intensity thatincreases on the plane perpendicular to the optical axis thereof along asecond direction opposite to the first direction.

The illumination unit may include a first illumination optical filteroperable to transmit light having the first wavelength and a secondillumination optical filter operable to transmit light having the secondand third wavelengths. In this case, the first and second illuminationoptical filters are arranged in such a manner that the first and secondillumination light beams are incident on the first and secondillumination optical filters, respectively.

The first illumination optical filter may have a transmittance thatincreases along a first direction on an incident surface thereof, whilethe second illumination optical filter have a transmittance thatincreases along a second direction on an incident surface thereof, thesecond direction being opposite to the first direction.

The first illumination optical filter may have a transmittance thatincreases or decreases with increase of a distance from the optical axisof the first illumination light beam on the incident surface thereof,while the second illumination optical filter has a transmittance that,with increase of a distance from the optical axis of the secondillumination light beam on the incident surface, decreases in a casewhere the transmittance of the first illumination optical filterincreases with the increase of the distance from the optical axis of thefirst illumination light beam or increases in a case where thetransmittance of the first illumination optical filter decreases withthe increase of the distance from the optical axis of the firstillumination light beam.

The separation unit may include a first outgoing optical filter operableto transmit light having the first wavelength, a second outgoing opticalfilter operable to transmit light having the second wavelength, and athird outgoing optical filter operable to transmit light having thethird wavelength. In this case, the first, second and third outgoingoptical filters are arranged in such a manner that the first, second andthird outgoing light beams are incident on the first, second and thirdout going optical filters, respectively.

The separation unit may include a first outgoing optical filter operableto transmit light having the first wavelength and a second outgoingoptical filter operable to transmit light having the second and thirdwavelengths. In this case, the first and second outgoing optical filtersare arranged in such a manner that the first outgoing light beam isincident on the first outgoing optical filter while the second and thirdoutgoing light beams are incident on the second outgoing optical filter.

The light-receiving unit may include a solid state image sensor, and theseparation unit may include a first outgoing optical filter thattransmits light having the first wavelength, a second outgoing opticalfilter that transmits light having the second wavelength and a thirdoutgoing optical filter that transmits light having the thirdwavelength, the first, second and third outgoing optical filters beingarranged alternately on a light-receiving surface of the solid stateimage sensor.

The depth calculation unit may calculate the depth-direction distance tothe subject by using a value based on the intensities of the second andthird outgoing light beams and the intensity of the first outgoing lightbeam.

The depth calculation unit may calculate the depth-direction distance tothe subject by using an averaged intensity of the intensities of thesecond and third outgoing light beams, and the intensity of the firstoutgoing light beam.

The second wavelength may be shorter than the first wavelength while thethird wavelength is longer than the first wavelength. In this case, theimage capturing apparatus may further comprise: an optically convergingunit operable to converge the outgoing light beams from the subject ontowhich the first and second illumination light beams are cast; aseparation unit operable to optically separate the outgoing light beamsinto a first outgoing light beam having the first wavelength and asecond outgoing light beam having the second and third wavelengths; alight-receiving unit operable to receive the first and second outgoinglight beams after being separated by the separation unit and convergedby the optically converging unit; and a light intensity detectoroperable to detect intensities of the first and second outgoing lightbeams received by the light-receiving unit, wherein the depthcalculation unit calculates the depth-direction distance to the subjectby using the intensities of the first and second outgoing light beams.

The depth calculation unit may calculate the depth-direction distance tothe subject by using the intensity of the first outgoing light beam anda half of the intensity of the second outgoing light beam.

The light intensity detector may calculate the intensities of the firstand second outgoing light beams for each pixel of an image of thesubject taken by the light-receiving unit. In this case, the depthcalculation unit calculates a depth distribution of the subject byobtaining the depth-direction distance to a region of the subjectcorresponding to every pixel.

The first and second illumination light beams may be light beams in aninfrared region, and the separation unit may further include a deviceoperable to optically separate visible light from the outgoing lightbeams from the subject. In this case, the light-receiving unit mayfurther include a solid state image sensor for visible light operable toreceive the visible light that is optically separated by the separationunit and is converged by the optically converging unit, and the imagecapturing apparatus may further comprise a recording unit operable torecord both the depth distribution of the subject calculated by thedepth calculation unit and the image of the subject taken by thesolid-state image sensor for visible light.

According to a second aspect of the present invention, a distancemeasuring method for obtaining information regarding a depth of asubject, comprises: an illumination step for simultaneously casting afirst illumination light beam mainly containing a first wavelength andhaving a first intensity distribution on a plane perpendicular to anoptical axis thereof and a second illumination light beam mainlycontaining a second wavelength and a third wavelength and having asecond intensity distribution on a plane perpendicular to an opticalaxis thereof onto the subject, the second and third wavelengths beingdifferent from the first wavelength, the second intensity distributionbeing different from the first intensity distribution; a separation stepfor optically separating outgoing light beams from the subject ontowhich the first and second illumination light beams are cast into afirst outgoing light beam having the first wavelength, a second outgoinglight beam having the second wavelength, and a third outgoing light beamhaving the third wavelength; a capturing step for capturing the first,second and third outgoing light beams; a light intensity detection stepfor detecting the intensities of the captured first, second and thirdoutgoing light beams; and a depth calculation step for calculating adepth-direction distance to the subject based on the intensities of thefirst, second and third outgoing light beams.

The depth-direction distance to the subject maybe calculated based on avalue based on the intensities of the second and third outgoing lightbeams and the intensity of the first outgoing light beam in the depthcalculation step.

The depth-direction distance to the subject maybe calculated based on anaveraged intensity of the intensities of the second and third outgoinglight beams and the intensity of the first outgoing light beam in thedepth calculation step.

According to a third aspect of the present invention, a distancemeasuring method for obtaining information regarding a depth of asubject, comprises: an illumination step for simultaneously casting afirst illumination light beam mainly containing a first wavelength andhaving a first intensity distribution on a plane perpendicular to anoptical axis of the first illumination light beam and a secondillumination light beam mainly containing a second wavelength and athird wavelength and having a second intensity distribution on a planeperpendicular to an optical axis of the second illumination light beamonto the subject, the second wavelength being shorter than the firstwavelength, the third wavelength being longer than the first wavelength,the second intensity distribution being different from the firstintensity distribution; a separation step for optically separating theoutgoing light beams into a first outgoing light beam having the firstwavelength and a second outgoing light beam having the second and thirdwavelengths; a capturing step for capturing the first and secondoutgoing light beams; a light intensity detection step for detecting theintensities of the first and second outgoing light beams; and a depthcalculation step for calculating a depth-direction distance to thesubject based on the intensities of the first and second outgoing lightbeams.

The depth-direction distance to the subject may be calculated based onthe intensity of the first outgoing light beam and a half of theintensity of the second outgoing light beam in the depth calculationstep.

According to a fourth aspect of the present invention, an imagecapturing apparatus for obtaining information regarding a depth of asubject, comprises: an illumination unit operable to cast a firstillumination light beam mainly containing a first wavelength and asecond illumination light beam mainly containing a second wavelength anda third wavelength, the first and second illumination light beams beingmodulated in such a manner that the intensities of the first and secondillumination light beams are changed along the respective travelingdirections, the second and third wavelengths being different from thefirst wavelength; and a depth calculation unit operable to calculate adepth-direction distance to the subject based on outgoing light beamsfrom the subject onto which the first and second illumination lightbeams are cast.

The first illumination light beam may be modulated in such a manner thatthe intensity thereof monotonously increases or decreases along thetraveling direction thereof, and the second illumination light beam maybe modulated in such a manner that the intensity thereof monotonouslydecreases along the traveling direction of the second illumination lightbeam when the intensity of the first illumination light beammonotonously increases along the traveling direction of the firstillumination light beam, or increases along the traveling direction ofthe second illumination light beam when the intensity of the firstillumination light beam monotonously decreases along the travelingdirection of the first illumination light beam.

The image capturing apparatus may further comprise a modulation unitoperable to change the intensities of the first and second illuminationlight beams by temporal modulation.

The second wavelength may be shorter than the first wavelength while thethird wavelength is longer than the first wavelength, and the imagecapturing apparatus may further comprise: an optically converging unitoperable to converge the outgoing light beams from the subject ontowhich the first and second illumination light beams are cast; aseparation unit operable to optically separate the outgoing light beamsinto a first outgoing light beam having the first wavelength and asecond outgoing light beam having the second and third wavelengths; alight-receiving unit operable to receive the first and second outgoinglight beams after being separated by the separation unit and convergedby the optically converging unit; and a light intensity detectoroperable to detect intensities of the first and second outgoing lightbeams received by the light-receiving unit, wherein the depthcalculation unit calculates the depth-direction distance to the subjectby using the intensities of the first and second outgoing light beams.

According to a fifth aspect of the present invention, a distancemeasuring method for obtaining information regarding a depth of asubject, comprises: an illumination step for simultaneously casting afirst illumination light beam mainly containing a first wavelength and asecond illumination light beam mainly containing a second wavelength anda third wavelength, the first and second illumination light beams beingmodulated in such a manner that the intensities of the first and secondillumination light beams are changed along traveling directions thereof,respectively; a separation step for optically separating the outgoinglight beams from the subject into a first outgoing light beam having thefirst wavelength, a second outgoing light beam having the secondwavelength, and a third out going light beam having the thirdwavelength; a capturing step for capturing the first, second and thirdoutgoing light beams; a light intensity detection step for detecting theintensities of the first, second and third outgoing light beams; and adepth calculation step for calculating a depth-direction distance to thesubject based on the intensities of the first, second and third outgoinglight beams.

The depth-direction distance to the subject may be calculated based onthe intensity of the first outgoing light beam and a value based on theintensities of the second and third outgoing light beams in the depthcalculation step.

According to a sixth aspect of the present invention, a distancemeasuring method for obtaining information regarding a depth of asubject, comprises: an illumination step for simultaneously casting afirst illumination light beam mainly containing a first wavelength and asecond illumination light beam mainly containing a second wavelength anda third wavelength, the first and second illumination light beams beingmodulated in such a manner that the intensities of the first and secondillumination light beams are changed along traveling directions thereof,respectively, the second wavelength being shorter than the firstwavelength, the third wavelength being longer than the first wavelength;a separation step for optically separating the outgoing light beams intoa first outgoing light beam having the first wavelength and a secondoutgoing light beam having the second and third wavelengths; a capturingstep for capturing the first and second outgoing light beams; a lightintensity detection step for detecting the intensities of the first andsecond outgoing light beams; and a depth calculation step forcalculating a depth-direction distance to the subject based on theintensities of the first and second outgoing light beams.

This summary of the invention does not necessarily describe allnecessary features of the present invention. The present invention mayalso be a sub-combination of the above described features. The above andother features and advantages of the present invention will become moreapparent from the following description of embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a basic principle of the firstembodiment of the present invention.

FIGS. 2A and 2B are diagrams for explaining intensity distributions ofillumination light.

FIG. 3 shows a structure of an image capturing apparatus according tothe first embodiment of the present invention.

FIG. 4 is a diagram for explaining an exemplary intensity distributionof the illumination light.

FIGS. 5A, 5B, 5C and 5D explain an optical filter 42 provided in anillumination unit 40.

FIG. 6 shows an exemplary arrangement of the illumination unit 40 and acapturing unit 100 according to the first embodiment of the presentinvention.

FIG. 7 shows a structure of a processing unit 110 according to the firstembodiment of the present invention.

FIG. 8 is a diagram for explaining a method for calculating adepth-direction distance to a subject 12.

FIGS. 9A and 9B are diagrams for explaining a method for obtaining adummy reflected-light intensity Wd by interpolation or extrapolation.

FIGS. 10A and 10B are diagrams for explaining a method for obtaining thedummy reflected-light intensities from the first and second reflectedlight.

FIG. 11 shows the surface reflectance of each of three kinds of objects.

FIG. 12 shows an optical filter provided on a light-receiving unit 60.

FIG. 13 is a flowchart of a distance measuring method according to thefirst embodiment of the present invention.

FIG. 14 is a flowchart of a depth calculation process S110.

FIG. 15 is a flowchart of a modification of the depth calculationprocess S110.

FIG. 16 shows another example of the arrangement of the illuminationunit 40 and the capturing unit 100 according to the first embodiment ofthe present invention.

FIG. 17 shows the structure of the processing unit 110 in the otherexample of the first embodiment of the present invention.

FIG. 18 is a diagram for explaining the depth-direction distancecalculating method in the other example of the first embodiment of thepresent invention.

FIG. 19 is a diagram for explaining the distance measuring method in theother example of the first embodiment of the present invention.

FIG. 20 shows still another example of the arrangement of theillumination unit 40 and the capturing unit 100 according to the firstembodiment of the present invention.

FIG. 21 shows the structure of the processing unit 110 in the otherexample of the first embodiment of the present invention.

FIGS. 22A, 22B, 22C, 22D and 22E are diagrams for explaining a basicprinciple of the second embodiment of the present invention.

FIG. 23 shows an arrangement of the illumination unit 40 and a capturingunit 100 according to the second embodiment of the present invention.

FIG. 24 is a flowchart of a distance measuring method according to thesecond embodiment of the present invention.

FIG. 25 is a flowchart of a depth calculation process S310.

FIG. 26 is a flowchart of a modification of the depth calculationprocess S310.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on the preferred embodiments,which do not intend to limit the scope of the present invention, butexemplify the invention. All of the features and the combinationsthereof described in the embodiment are not necessarily essential to theinvention.

Embodiment 1

FIG. 1 is a diagram for explanation of the principle of the firstembodiment of the present invention. A light source 26 emits a firstillumination light beam 16 and a second illumination light beam 18. Thefirst and second illumination light beams 16 and 18 have the first andsecond intensity distributions on planes perpendicular to optical axesthereof, respectively. When the light source 26 casts the firstillumination light beam 16 onto the subject 12, a camera 28 captures afirst reflected light beam 22 from an illuminated portion 14 that isilluminated with the first illumination light beam 16. Then, when thelight source 26 casts the second illumination light beam 18 onto thesubject 12, the camera 28 captures a second reflected light beam 24 fromthe illuminated portion 14 that is illuminated with the secondillumination light beam 18. The camera 28 maybe a charge-coupled device(CCD) image sensor, for example, and captures the first and secondreflected light beams 22 and 24 from the illuminated portion 14 of thesubject 12 for every pixel so as to detect the intensity of the firstand second reflected light beam 22 and 24 for every pixel. The camera 28is arranged at a position apart from the light source 26 by apredetermined distance L1.

FIG. 2A illustrates exemplary distributions of the intensities Wa and Wdon the planes perpendicular to the optical axes of the first and secondillumination light beams 16 and 18, respectively. More specifically,FIG. 2A shows the distributions of the intensities Wa and Wd on theplanes perpendicular to the optical axes of the first and secondillumination light beams 16 and 18, respectively. The vertical axisrepresents the intensity while the horizontal axis represents the degreeof an angle formed by a line connecting the light source 26 to thecamera 28 shown in FIG. 1 and the respective illumination light beamhaving the corresponding intensity represented by the horizontal axis.In this example, the intensity Wa of the first illumination light beam16 monotonously increases in the first direction on the planeperpendicular to the optical axis of the first illumination light beam16, while the intensity Wd of the second illumination light beam 18monotonously increases in a direction opposite to the first direction onthe plane perpendicular to the optical axis of the second illuminationlight beam 18. FIG. 2B shows the intensity ratio of Wa to Wd.

In a case where the first and second illumination light beams 16 and 18have the intensity distributions as shown in FIG. 2A, an illuminationangle θ2 (FIG. 1) of a direction along which the first and secondillumination light beams 16 and 18 travel with respect to the lineconnecting the light source 26 and the camera 28 is calculated based onthe intensity ratio Wa/Wd detected at each pixel of the camera 28, asshown in FIG. 2B. Also, an incident angle θ1 (FIG. 1) of the first andsecond reflected light beams 22 and 24 with respect to the lineconnecting the light source 26 and the camera 28 is calculated from theposition of the pixel at which the intensity ratio Wa/Wd is detected.Thus, from the incident angle θ1, the illumination angle θ2, and adistance L1 between the light source 26 and the camera 28, adepth-direction distance to the illuminated portion 14 of the subject 12can be calculated by triangulation.

In the above-mentioned method, however, since the first and second lightbeams 16 and 18 are cast one by one and the camera 28 receives the lightbeams reflected from the subject 12, time difference occurs in the imagecapturing. Thus, the above-mentioned method cannot be applied to a caseof the moving subject. In order to overcome this problem, a method isconsidered in which the first and second illumination light beams 16 and18 are provided with different wavelength characteristics and areemitted simultaneously. In this method, the first and second reflectedlight beams 22 and 24 are separated from each other by wavelength andthen the intensity of each reflected light beam is measured.

In general, the surface reflectance of the illuminated portion of thesubject varies depending on the wavelength of the light beam that iscast onto the illuminated portion. Thus, even if the reflected-lightintensity ratio Wa/Wd has been obtained, the depth-direction distance ofthe subject cannot be calculated. Although the reflected-light intensityratio Wa/Wd and the depth-direction distance to the illuminated portion14 of the subject 12 can be obtained while the difference between thewavelength λ1 of the first illumination light beam 16 and the wavelengthλ2 of the second illumination light beam 18 is made very small and thedifference of the surface reflectance between wavelengths is ignored,the calculation result includes an error. In order to reduce such acalculation error, the difference between the wavelengths λ1 and λ2 hasto be made sufficiently small. However, when the difference between thewavelengths λ1 and λ2 is made small, the precision in the wavelengthseparation is also reduced, so that the intensity measurement for therespective wavelengths may include an error.

Therefore, the design of the apparatus is in dilemma as to whether tomake the difference between the wavelengths λ1 and λ2 larger in order toimprove the resolution of the wavelength separation thereby improvingthe precision of the intensity measurement or to make the differencebetween the wavelengths λ1 and λ2 smaller in order to reduce thedifference of the surface reflectance between wavelengths therebyimproving the precision of the distance measurement. Thus, there is alimitation in improvement of the precision of the distance measurement.

Accordingly, in the present embodiment, the depth-direction distance tothe subject can be obtained in the following manner. The firstillumination light beam having the first wavelength component as a maincomponent and the first intensity distribution on a plane perpendicularto an optical axis of the first illumination light beam and the secondillumination light beam having the second and third wavelengthcomponents as main components and the second intensity distribution on aplane perpendicular to an optical axis of the second illumination lightbeam are cast onto the subject simultaneously, the second and thirdwavelength components being different from the first wavelengthcomponent and the second intensity distribution being different from thefirst intensity distribution. Then, the first and second reflected lightbeams respectively generated by reflection of the first and secondillumination light beams by the subject are optically separated, andthereafter a dummy reflected-light intensity is calculated from thesecond reflected light beam. The dummy reflected-light intensity is theintensity of a dummy reflected light beam expected to be obtained fromthe subject in a case where it is assumed that light having the secondintensity distribution mainly contains the first wavelength. Based on aratio of the dummy reflected-light intensity and the intensity of thefirst reflected light beam, and the distance L1 between the light source26 and the camera 28, the depth-direction distance to the illuminatedportion 14 of the subject 12 is calculated. In this method, thedifference of the surface reflectance between the wavelengths can becancelled by obtaining the dummy reflected-light intensity. Thus, thedepth of the subject or the distance to the subject can be preciselyobtained.

FIG. 3 schematically shows a structure of an image capturing apparatus200 according to the first embodiment of the present embodiment. Theimage capturing apparatus 200 includes an illumination unit 40, acapturing unit 100, a controller 90 and a processing unit 110.

The illumination unit 40 casts light onto the subject 12. The capturingunit 100 captures an image of the subject 12 that is illuminated withthe light from the illumination unit 40. The processing unit 110processes the image of the subject 12 taken by the capturing unit 100 toobtain the depth of or the distance to the captured subject 12, so thatthe obtained depth or distance is recorded as information regarding adepth distribution of the subject 12. The processing unit 110 can alsorecord the image of the subject 12 taken by the capturing unit 100. Thecontroller 90 perform a feedback control based on the depth-directiondistance to the subject 12 obtained by the processing unit 110 so as tocontrol at least one of the intensity, an emission time, a duration ofthe emission and an emission position of the light emitted from theillumination unit 40, an exposure period of the capturing unit 100 andthe like.

The illumination unit 40 includes a light-source unit 44 and opticalfilters 42 a and 42 b. The light beams emitted from the light-sourceunit 44 pass through the optical filters 42 a, 42 b so as to be incidenton the subject 12 as the first and second illumination light beams 16and 18. The optical filer 42 a allows light having the first wavelengthλ1 to pass therethrough, while the optical filter 42 b allows lighthaving the second wavelength λ2 and the third wavelength λ3 to passtherethrough. The first illumination light beam 16 has the firstintensity distribution on the plane perpendicular to the optical axis ofthe first illumination light beam 16, while the second illuminationlight beam 18 has the second intensity distribution different from thefirst intensity distribution on the plane perpendicular to the opticalaxis of the second illumination light beam 18. The first and secondintensity distributions are determined by transmittance distributions ofthe optical filters 42 a and 42 b described later, the transmittancedistributions of the optical filters 42 a and 42 b being different fromeach other.

In order to efficiently use the light amount, the illumination unit 40may include an optical lens, such as a condenser lens, inserted onoptical paths of the illumination light beams for converging the lightbeams.

The capturing unit 100 includes an optical lens 46 as an opticalconverging unit, a separation unit 50 and a light-receiving unit 60. Theoptical lens 46 converges the reflected light 48 from the subject 12.The separation unit 50 separates the reflected light 48 from the subject12 into wavelength components in accordance with the wavelengthcharacteristics of the light beams emitted from the illumination unit40. The light-receiving unit 60 receives the reflected light beams afterbeing converged by the optical lens 46 and separated by the separationunit 50.

The light-receiving unit 60 is a solid-state image sensor, for example.The image of the subject is formed on a light-receiving surface of thesolid state image sensor. In accordance with the light amount of theformed image of the subject, respective sensor elements of the solidstate image sensor are electrically charged. The stored charges arescanned in a predetermined order, so that the charges are read as anelectric signal.

It is desirable that the solid state image sensor be a charge-coupleddevice (CCD) image sensor having an excellent S/N ratio and a largenumber of pixels so as to allow the intensity of the reflected lightfrom the subject to be detected with high precision for each pixel. Asthe solid state image sensor, any of an MOS image sensor, a CdS-Secontact image sensor, an a-Si (amorphous silicon) contact image sensor,and a bipolar contact image sensor may be used other than the CCD imagesensor.

The processing unit 110 includes an image memory 54, a light intensitydetector 70, a depth calculation unit 80, an image correction unit 56and a recording unit 58. The image memory 54 stores the image of thesubject 12 taken by the capturing unit 100 in accordance with thewavelength characteristics of the illumination light emitted from theillumination unit 40. The light intensity detector 70 detects theintensity of the reflected light from the image of the subject 12 storedin the image memory 54 for each pixel or pixel area. The depthcalculation unit 80 calculates the depth-direction distance to thesubject 12 that is captured in each pixel area based on thereflected-light intensity detected by the light intensity detector 70.The recording unit 58 records the distribution of the depth of thesubject 12 calculated by the depth calculation unit 80. The imagecorrection unit 56 conducts correction such as gray-scale correction orcorrection of white balance for the image of the subject 12 stored inthe image memory 54. The recording unit 58 records the image of thesubject 12 processed by the image correction unit 56. Moreover, thelight intensity detector 70 and the depth calculation unit 80 output thedetected level of the reflected light from the subject 12 and theinformation of the depth distribution of the subject 12 to thecontroller 90, respectively. The recording unit 58 records image dataand the depth-distribution information onto a semiconductor memory suchas a flash memory or a memory card.

The controller 90 conducts a feed-back control based on thedepth-direction distance to the subject 12 obtained by the processingunit 110 so as to control the intensity of the illumination lightemitted by the illumination unit 40, the emission time, the sensitivityor an exposure time period of the light-receiving unit 40 of thecapturing unit 120, or the like. The controller 90 may control theillumination unit 40 and the capturing unit 100 by using luminance datafrom a luminance sensor (not shown) and/or distance data from a distancesensor (not shown). Also, the controller 90 may adjust a focal length,an aperture size, the exposure time period or the like when the image ofthe subject 12 is to be captured, based on the depth-direction distanceto the subject 12 obtained by the processing unit 110.

FIG. 4 is a diagram for explaining an exemplary intensity distributionof the light emitted from the illumination unit 40. A plane 66 isperpendicular to an optical axis 64 of the light emitted from theillumination unit 40. On the plane 66, the light emitted from theillumination unit 40 monotonously increases or decreases in a directionshown by a line 68 in FIG. 4. The line 68 is parallel to a line obtainedby projecting a line 62 connecting the illumination unit 40 and thelight-receiving unit or optical converging unit 72 onto the plane 66. Inthe present embodiment, the depth of the subject or the distance to thesubject is calculated by triangulation based on the distance between theillumination unit 40 and the capturing unit (the light receiving unit orthe optical converging unit), the illumination angle of the lightemitted from the illumination unit, and the incident angle of thereflected light. Thus, it is preferable that the first and secondillumination light beams emitted from the illumination unit 40 have theintensity distributions described with reference to FIG. 4. In analternative example, the first illumination light may have the intensitydistribution that monotonously increases or decreases with the increaseof the distance from the optical axis of the first illumination lightbeam on the plane perpendicular to the optical axis. In this case, thesecond illumination light beam may have the intensity distribution inwhich the intensity monotonously decreases with the increase of thedistance from the optical axis of the second illumination light beam onthe plane perpendicular to the optical axis in a case where theintensity of the first illumination light beam monotonously increaseswith the increase of the distance from the optical axis of the firstillumination light beam, or monotonously increases with the increase ofthe distance from the optical axis of the second illumination light beamin a case where the intensity of the first illumination light beammonotonously decreases with the increase of the distance from theoptical axis of the first illumination light beam. In anotheralternative example, the first and second illumination light beams mayhave intensity distributions other than those described above.

FIGS. 5A, 5B, 5C and 5D are diagrams for explaining examples of theoptical filter 42 in the present embodiment. FIGS. 5A and 5B arediagrams for explaining the optical filter 42 having the transmittancevarying along a single direction. As described above with reference toFIG. 3, the illumination unit includes two optical filters 42 havingdifferent transmittance distributions. One of the optical filters 42 hasthe transmittance distribution in which the transmittance monotonouslyincreases along a certain direction, as shown in FIG. 5A, while theother has the transmittance distribution in which the transmittancemonotonously increases along a direction opposite to the certaindirection, as shown in FIG. 5B. Alternatively, one of the opticalfilters 42 may have such a transmittance distribution that thetransmittance monotonously increases with the increase of the distancefrom the center of the optical filter while the other may have such atransmittance distribution that the transmittance monotonously decreaseswith the increase of the distance from the center of the optical filter.Moreover, an optical filer having another transmittance distribution maybe used. In addition, it is preferable that the optical filters 42 allowdifferent wavelength components to mainly pass therethrough,respectively.

In a case of using the optical filter 42 described with reference toFIGS. 5C and 5D, it is possible to perform distance calculation in alldirections. In this case, however, an error occurs in directions otherthan the direction parallel to the line connecting the illumination unit40 and the capturing unit 100, since the distance calculation usestriangulation. Thus, it is preferable in the present embodiment to usethe optical filter 42 described with reference to FIGS. 5A and 5B.

FIG. 6 shows an exemplary arrangement of the illumination unit 40 andthe capturing unit 100 in the present embodiment. The illumination unit40 includes the light-source unit 44 and the optical filters 42 a and 42b. The optical filter 42 a mainly transmits light having a wavelength λawhile the optical filter 42 b mainly transmits light having wavelengthsλb and λc. The illumination unit 40 casts the light emitted from thelight-source unit 44 onto the subject 12 via the optical filters 42 aand 42 b as the light having the wavelength λa and the light having thewavelengths λb and λc.

The optical lens 46 of the capturing unit 100 converges the lightreflected from the illuminated portion 14 of the subject 12. Theseparation unit 50 is a prism that optically separates the reflectedlight into three wavelength components λa, λb and λc to separate opticalpaths. The light-receiving units 60 a, 60 b and 60 c are three panels ofsolid state image sensors. The light beams having the wavelengths λa, λband λc separated by the separation unit 50 are received by thelight-receiving units 60 a, 60 b and 60 c, respectively. The light beamreceived by each light-receiving unit is read as the electric charges bya photoelectric effect. The electric charges are converted into adigital electric signal by an A-D converter (not shown) to be input tothe processing unit 110.

FIG. 7 shows the structure of the processing unit 110 in the presentembodiment. The images of the subject output from the light-receivingunits 60 a, 60 b and 60 c are stored in image memories 54 a, 54 b and 54c, respectively. The light intensity detector 70 detects thereflected-light intensity for each of the wavelengths λa, λb and λc byusing the image data stored in the respective image memories 54 a, 54 band 54 c. The depth calculation unit 80 obtains the distance from theillumination unit 40 to the illuminated portion 14 of the subject 12 byusing the reflected-light intensities for the wavelengths λa, λb and λcdetected by the light intensity detector 70 and the distance from theillumination unit 40 to the optical lens (optical converging unit) 46 orthe light-receiving unit 60. The depth calculation unit 80 calculates,for each pixel or pixel area of the captured image, the depth-directiondistance to the subject 12 captured in the pixel or the pixel area,thereby obtaining the depth distribution of the subject 12. The depthdistribution thus obtained is output from the depth calculation unit 80to be recorded by the recording unit 58.

The light intensity detector 70 outputs the reflected-light intensitiesfor the wavelengths λa, λb and λc to the controller 90. The depthcalculation unit 80 outputs the depth-distribution information of thesubject 12 to the controller 90. The controller 90 adjusts the intensityof the light emitted from the light-source unit 44, if the intensitylevel is not appropriate.

FIG. 8 is a diagram for explaining a method of calculating thedepth-direction distance by the light intensity detector 70 and thedepth calculation unit 80. The first illumination light beam that mainlycontains the component of the wavelength λa and has the first intensitydistribution and the second illumination light beam that mainly containsthe components of the wavelengths λb and λc and has the second intensitydistribution different from the first intensity distribution are castonto the subject 12 (not shown), and the light beams reflected from thesubject 12 are than received by the light-receiving unit 60.

The light intensity detector 70 detects the intensity Wa of thereflected light having the wavelength λa, the intensity Wb of thereflected light having the wavelength λb and the intensity Wc of thereflected light having the wavelength λc. The depth calculation unit 80obtains a dummy reflected-light intensity Wd that is expected to beobtained in a case where it is assumed that the second illuminationlight beam mainly contains the component of the wavelength λa and hasthe second intensity distribution, by using the intensity Wb of thereflected light having the wavelength λb and intensity Wc of thereflected light having the wavelength λc. Then, a ratio Wa/Wd of theactual reflected-light intensity Wa to the dummy reflected-lightintensity Wd is calculated, so as to calculate the distance to thesubject 12 or the depth of the subject 12 based on the distance from theillumination unit 40 (not shown) to the optical lens 46 (not shown) orthe light-receiving unit 60 and the intensity ratio Wa/Wd.

Both the actual reflected-light intensity Wa and the dummyreflected-light intensity Wd are obtained for the wavelength λa. Thus,adverse effects of the difference of the surface reflectance of theilluminated portion 14 of the subject 12 between wavelengths can becancelled. Moreover, since the dummy reflected-light intensity Wd iscalculated from the actual reflected-light intensities Wb and Wcobtained for the wavelengths λb and λc that are different from thewavelength λa, the error that may cause in the wavelength-separation canbe reduced by setting the interval between the wavelengths so as to makethe separation of the components of the wavelengths λa, λb, and λceasier, thus the aforementioned dilemma can be eliminated.

It should be noted that there are many modifications of the calculationmethod for obtaining the dummy reflected-light intensity Wd by using theintensities Wb and Wc of the reflected light beams having thewavelengths λb and λc.

FIG. 9 is a diagram for explaining an exemplary method for obtaining thedummy reflected-light intensity Wd by interpolation or extrapolation. Inthis method, the dummy reflected-light intensity Wd for the wavelengthλa is obtained by interpolation or extrapolation of the reflected-lightintensity Wb for the wavelength λb and the reflected-light intensity Wcfor the wavelength λc. A middle value between the reflected-lightintensity Wb for the wavelength λb and the reflected-light intensity Wcfor the wavelength λc may be simply used as the dummy reflected-lightintensity Wd with the wavelengths λa, λb and λc set in such a mannerthat the wavelength λa is equal to the middle value between thewavelengths λb and λc, as shown in FIG. 9A. Alternatively, the dummyreflected-light intensity Wd may be obtained by extrapolation or linearapproximation, as shown in FIG. 9B.

FIGS. 10A and 10B are diagrams for explaining an exemplary method forobtaining the dummy reflected-light intensity from the first and secondreflected light beams. In a case where the first reflected light beammainly contains the wavelengths λ1 and λ2 while the second reflectedlight beam mainly contains the wavelengths λ3 and λ4, linearinterpolation is performed for the intensities for the respectivewavelengths so as to calculate the dummy reflected-light intensity Waand Wd, as shown in FIGS. 10A and 10B. Although the exemplary methodsare described with reference to FIGS. 9A to FIG. 10B, the method forcalculating the dummy reflected-light intensity cannot be limited tothose described with reference to FIGS. 9A to 10B.

It is preferable in any of the above-mentioned methods that thewavelengths λb and λc are set to values closer to each other so that itis possible to perform linear interpolation or linear extrapolation forthe wavelengths λb and λc, in order to obtain the dummy reflected-lightintensity precisely.

FIG. 11 shows the surface reflectance of each of three kinds of objects.The horizontal axis represents the wavelength while the vertical axisrepresents the reflectance. Graphs 202, 204 and 206 respectively showresults of surface reflectance measurements for the three kinds ofobjects, i.e., skin, a road and a leaf, by a spectrometer. In awavelength region containing 650 nm and wavelengths in the vicinitythereof, interpolation or extrapolation can be performed for any of thethree kinds of objects with a considerable precision, as shown by markson the graphs. Thus, it is preferable to select wavelengths for whichinterpolation or extrapolation can be performed as the wavelengths λa,λb and λc. Moreover, when image correction such as gray-scalecorrection, that is performed in a typical digital camera, is performedfor the output signal from the solid state image sensor of thelight-receiving unit 40, the linearity of the signal is lost. Therefore,it is preferable that the intensity is detected at a phase where thesignal intensity has the linearity for the intensity of the lightincident on the solid state image sensor and thereafter interpolation isperformed. Alternatively, a table showing an inverse function of asignal-conversion function by the image correction such as thegray-scale correction may be prepared in advance. In this case, thesignal output after being subjected to the image correction is convertedinto the signal intensity having the linearity for the intensity of thelight incident on the solid state image sensor with reference to theinverse-function table. Then, the intensity detection is performed andinterpolation is performed.

In the above description, an optical device for splitting the opticalpath by separation of the light into wavelength components, such as aprism, is used as the separation unit 50. However, an optical filterarranged on the light-receiving surface of the light-receiving unit 60may be used as the separation unit 50.

FIG. 12 is a diagram for explaining an optical filter that onlytransmits a specific wavelength component provided on thelight-receiving unit 60. As the light-receiving unit 60, a single panelof solid state image sensor 84 is used. On the light-receiving surfaceof the solid state image sensor 84 is arranged the optical filter 74.The optical filter 74 includes filter portions that only transmit lightbeams having the wavelengths λa, λb and λc, respectively, that arealternately arranged. Such an arrangement of the optical filter 84 makesit possible to find out which of the light beams having the wavelengthsλa, λb and λc is received by a pixel of the solid state image sensor 84,thereby the light beams having the wavelengths λa, λb and λc can bereceived while being separated from each other. In this case, the sizeof the whole apparatus can be reduced as compared to a case of using theprism, because the reflected light is received by the single panel ofthe solid state image sensor 84.

In the above description of the embodiment, in a case where the surfacereflectance of the subject largely depends on the wavelength of theillumination light, it is desirable that the wavelengths λa, λb and λcare set as close as possible in order to prevent occurrence of the errorin the calculation of the dummy reflected-light intensity. On the otherhand, in order to improve the precision of the detection of thereflected-light intensity for the respective wavelengths, it isdesirable that inclusion of the components having a wavelength otherthan the wavelengths λa, λb and λc is made as little as possible orinterference between the wavelengths is made as little as possible bysetting the wavelengths λa, λb and λc to be values apart from each otherso as to improve the resolution of the wavelengths λa, λb and λc.Therefore, it is preferable to design the wavelength characteristics ofthe light-source unit 44, the wavelength-transmission characteristics ofthe optical filters, and the wavelength-transmission characteristics ofthe separation unit 50 of the capturing unit 100 in accordance with thesurface-reflectance characteristics of the subject and/or the requiredmeasurement precision.

FIG. 13 is a flowchart of the distance measuring method according to thepresent embodiment. The illumination unit 40 casts the firstillumination light beam that mainly contains the wavelength λa and hasthe first intensity distribution on the plane perpendicular to theoptical axis of the first illumination light beam and the secondillumination light that mainly contains the wavelengths λb and λc bothdifferent from the wavelength λa and has the second intensitydistribution on the plane perpendicular to the optical axis thereof ontothe subject 12 simultaneously (S100).

The optical lens 46 of the capturing unit 100 converges the reflectedlight from the subject 12 that is illuminated with the first and secondillumination light beams (S102).

The separation unit 50 separates the reflected light from the subject 12into the first reflected light beam having the wavelength λa, the secondreflected light beam having the wavelength λb and the third reflectedlight beam having the wavelength λc (S104).

The light-receiving unit 60 receives the first, second and thirdreflected light beams (S106). The light intensity detector 70 of theprocessing unit detects the intensities Wa, Wb and Wc of the first,second and third reflected light beams (S108).

The depth calculation unit 80 calculates the depth-direction distance tothe subject 12 by using the intensities Wa, Wb and Wc of the first,second and third reflected light beams and the distance from theillumination unit 40 to the optical lens 46 or the light-receiving unit60 (S110).

FIG. 14 is a flowchart of the calculation process of the depth-directiondistance S110. First, the dummy reflected-light intensity Wd in a caseof assuming that the light containing the wavelength λa has the secondintensity distribution is obtained based on the intensities Wb and Wc ofthe second and third reflected light beams (S112).

The dummy reflected-light intensity Wd is obtained by interpolation orextrapolation of the intensities Wb and Wc of the second and thirdreflected light beams. Then, the ratio Wa/Wd of the intensity Wa of thefirst reflected light beam to the dummy reflected-light intensity Wd isobtained (S114). Based on the intensity ratio Wa/Wd, the distance fromthe illumination unit 40 to the optical lens 46 or the light-receivingunit 60, and the position of the pixel that provides the reflected-lightintensity ratio Wa/Wd, the distance to the subject 12 is calculated(S116).

FIG. 15 is a flowchart of an example of the calculation process of thedepth-direction distance S110. First, an average intensity Wd=(Wb+Wc)/2of the intensities Wb and Wc of the second and third reflected lightbeams is obtained (S118). Then, the ratio Wa/Wd of the intensity Wa ofthe first reflected light beam to the averaged intensity Wd of thesecond and third reflected light beams is obtained (S120). Based on thereflected-light intensity ratio Wa/Wd, the distance from theillumination unit 40 to the optical lens 46 or the light-receiving unit60 of the capturing unit 100, and the position of the pixel of thecapturing unit 100 that provides the reflected-light intensity ratioWa/Wd thus obtained, the distance to the subject 12 is calculated(S122).

As described above, according to the image capturing apparatus of thepresent embodiment, the illumination light beams having differentwavelength characteristics and different intensity distributions arecast onto the subject simultaneously. The light reflected from thesubject is separated into wavelength components in accordance with thewavelength characteristics. Then, the depth-direction distance to thesubject can be easily obtained by using the intensities of the reflectedlight beams separated from each other.

In addition, since the image of the subject carried by the reflectedlight is captured in the solid state image sensor and is then stored asimage data, the depth-direction distance can be calculated by detectingthe reflected-light intensity for each pixel or pixel area. Thus, thedepth distribution of the region of the subject that is captured can beobtained. Accordingly, the depth distribution of the subject can beobtained from a two-dimensional image of the subject so as to create athree-dimensional image of the subject.

FIG. 16 illustrates another exemplary structure of the image capturingapparatus according to the first embodiment. The image capturingapparatus of the present example is the same as that of that describedwith reference to FIG. 6 except for the arrangement of the illuminationunit 40 and the capturing unit 100, and therefore the description forthe same components is omitted and only the illumination unit 40 and thecapturing unit 100 are described below. FIG. 16 is a diagram showing thearrangement of the illumination unit 40 and the capturing unit 100 inthe present example. In the present example, the optical filter 42 a ofthe illumination unit 40 transmits light mainly containing a wavelengthλa, while the optical filter 42 b transmits light mainly containing awavelength λb shorter than the wavelength λa and light having awavelength λc longer than the wavelength λa. The illumination unit 40casts the first illumination light beam that mainly contains thewavelength λa and has the first intensity distribution on the planeperpendicular to the optical axis of the first illumination light beamand the second illumination light beam that mainly contains thewavelengths λb and λc and has the second intensity distribution on theplane perpendicular to the optical axis of the second illumination lightbeam onto the illuminated portion 14 of the subject 12 simultaneously.The separation unit 50 of the capturing unit 100 is a prism thatseparates the light beam mainly containing the wavelength λa from thelight beam mainly containing the wavelengths λb and λc to split theoptical paths thereof. The light-receiving units 60 a and 60 b are twopanels of solid state image sensors. The light beam having thewavelength λa separated by the separation unit 50 is received by thelight-receiving unit 60 a, while the light beam having the wavelengthsλb and λc is received by the light-receiving unit 60 b. The light beamsreceived by the light-receiving units 60 a and 60 b are converted intoelectric signals to be input to the processing unit 110, respectively.

FIG. 17 is a diagram showing the structure of the processing unit 110 inthe present example. The images of the subject output from thelight-receiving units 60 a and 60 b are stored in the image memories 54a and 54 b, respectively. The light intensity detector 70 detects theintensity of the reflected light having the wavelength λa and theintensity of the reflected light having the wavelengths λb and λc byusing the image data stored in the respective image memories 54 a and 54b. The depth calculation unit 80 obtains the depth of or the distance tothe illuminated portion 14 of the subject 12 by using the intensity ofthe reflected light having the wavelength λa and the intensity of thereflected light having the wavelengths λb and λc detected by the lightintensity detector 70. The depth calculation unit 80 calculates, foreach pixel or pixel area, the depth-direction distance to theilluminated portion 14 of the subject 12 taken in the pixel or the pixelarea so as to obtain the depth distribution of the subject 12. Theobtained depth-distribution information is output to the recording unit58. The recording unit 58 records the depth-distribution information.

FIG. 18 is a diagram for explaining the depth-direction distancecalculation method by the light intensity detector 70 and the depthcalculation unit 80. The light intensity detector 70 detects theintensity Wa of the reflected light having the wavelength λa and theintensity We of the reflected light having the wavelengths λb and λc.The depth calculation unit 80 sets Wd to a half value of the intensityWe of the reflected light having the wavelengths λb and λc. Since thewavelength λa is a middle value between the wavelengths λb and λc, thevalue of Wd is approximately equal to the dummy reflected-lightintensity obtained in a case of assuming that the light having thewavelength λa and having the second intensity distribution is cast ontothe illuminated portion 14 of the subject 12. Then, the intensity ratioWa/Wd of the actual reflected-light intensity Wa to the dummyreflected-light intensity Wd is calculated, and thereafter thedepth-direction distance to the subject is calculated based on thedistance from the illumination unit 40 (not shown) to the optical lens46 (not shown) or the light-receiving unit 60 and the intensity ratioWa/Wd.

Both of the reflected-light intensity Wa and the dummy reflected-lightintensity Wd are obtained for the wavelength λa, the adverse effect ofthe difference of the surface reflectance of the illuminated portion ofthe subject 12 between the wavelengths can be cancelled. Moreover, thedummy reflected-light intensity Wd is obtained from the intensities ofthe reflected light mainly containing the wavelengths λb and λc bothdifferent from the wavelength λa, the error that may occur in thewavelength-separation can be reduced by setting an interval between thewavelengths so as to allow easier wavelength-separation.

In order to obtain the dummy reflected-light intensity Wd precisely, itis preferable that the wavelength λa is the middle wavelength of thewavelengths λb and λc. In the above description, the separation unit 50separates the light having the wavelength λa from the light having thewavelengths λb and λc. However, it is not necessary to selectivelytransmit the light having the wavelengths λb and λc for the purpose offiltering. The same effects as those described above can be obtained ina case of using a band-cut filter that cuts the light having thewavelength λa.

FIG. 19 is a flowchart of the distance measuring method of the presentexample. The illumination unit 40 casts the first illumination lightcontaining main wavelength component λa and having the first intensitydistribution on the plane perpendicular to the optical axis of the firstillumination light beam and the second illumination light containing themain wavelength components λb and λc and having the second intensitydistribution on the plane perpendicular to the optical axis of thesecond illumination light beam onto the subject 12 simultaneously(S200). Please note that the wavelengths λb is shorter than thewavelength λa while the wavelength λc is longer than the wavelength λa.

The optical lens 46 converges the reflected light from the subject 12that is illuminated with the first and second illumination light beams(S202). The separation unit 50 optically separates the reflected lightfrom the subject 12 into the first reflected light beam having thewavelength λa and the second reflected light beam having the wavelengthsλb and λc (S204).

The light-receiving unit 60 receives the separated first and secondreflected light beams (S206). The light intensity detector 70 detectsthe intensities Wa and We of the first and second reflected light beams(S208).

The depth calculation unit 80 obtains the ratio Wa/Wd of the intensityWa of the first reflected light beam to a half Wd of the intensity We ofthe second reflected light beam (S210), and calculates the distance tothe subject 12 based on the reflected-light intensity ratio Wa/Wd, thedistance from the illumination unit 40 to the optical lens 46 or thelight-receiving unit 60 of the capturing unit 100, and the position ofthe pixel of the capturing unit 100 that provides the reflected-lightintensity Wa/Wd (S212).

As described above, according to the image capturing apparatus of thepresent example, the first illumination light beam having the firstwavelength as the main component and the first intensity distribution onthe plane perpendicular to the optical axis of the first illuminationlight beam and the second illumination light mainly having the secondand third wavelengths between which the first wavelength exists as themiddle wavelength and the second intensity distribution different fromthe first intensity distribution are cast onto the subjectsimultaneously. The reflected light from the subject is then separatedinto the first reflected light beam having the first wavelength and thesecond reflected light beam having the second and third wavelengths.Based on the ratio of the intensity of the first reflected light beam toa half of the intensity of the second reflected light beam, thedepth-direction distance to the subject can be calculated. Since thedummy reflected-light intensity in a case where the light containing thefirst wavelength has the second intensity distribution can be obtainedonly by obtaining a half of the intensity of the second reflected lightbeam, it is possible to calculate the depth-direction distance to thesubject very easily. In addition, according to the present example,since the number of the solid state image sensors for receiving thereflected light from the subject can be reduced to two, the size of thewhole apparatus can be reduced.

FIG. 20 illustrates still another exemplary structure of the imagecapturing apparatus according to the first embodiment. The imagecapturing apparatus in the present example is the same as that describedwith reference to FIG. 6 except for the arrangement of the illuminationunit 40 and the capturing unit 100. Therefore, the description for thesame components as those in FIG. 6 is omitted but only illumination unit40 and the capturing unit 100 are described below. FIG. 20 is a diagramshowing the arrangement of the illumination unit 40 and the capturingunit 100 in the present example. In the present example, the light beamsemitted from the illumination unit 40 are infrared light beams. Theoptical filter 42 a transmits light having a wavelength λa in aninfrared region while the optical filter 42 b transmits light havingwavelengths λb and λc in the infrared region. The illumination unit 40casts the first illumination light containing the main wavelengthcomponent λa and the first intensity distribution on the planeperpendicular to the optical axis of the first illumination light beamand the second illumination light containing the main wavelengthcomponents λb and λc and the second intensity distribution on the planeperpendicular to the optical axis of the second illumination light beamonto the subject 12 simultaneously. The first intensity distribution andthe second intensity distribution are different from each other. Thesubject 12 is also illuminated with other light having wavelengths in avisible region, for example, natural light or light from lighting.

The separation unit 50 of the capturing unit 100 is a prism forseparating the light having the wavelength λa in the infrared region,the light having the wavelengths λb and λc in the infrared region andthe light having wavelengths in the visible region so as to splitoptical paths from each other. The light-receiving units 60 a, 60 b and60 c are three panels of solid state image sensors. The light having thewavelength λa, the light having the wavelengths λb and λc, and the lightin the visible region are received by the light-receiving units 60 a, 60b and 60 c, respectively. In order to prevent the captured images by thelight in the infrared region from being out of focus, thelight-receiving units 60 a and 60 b are adjusted in advance so as toform the images in focus. The light beams received by thelight-receiving units 60 a, 60 b and 60 c are converted into electricsignals to be input to the processing unit 110, respectively.

FIG. 21 is a diagram showing the structure of the processing unit 110 inthe present example. The images of the subject output from thelight-receiving units 60 a and 60 b are stored in the image memories 54a and 54 b, respectively. The light intensity detector 70 detects thereflected-light intensities by using the image data stored in therespective image memories 54 a and 54 b, and the depth calculation unit80 obtains the depth-direction distance to the subject 12 by using thereflected-light intensities detected by the light intensity detector 70.The operations of the light intensity detector 70 and the depthcalculation unit 80 are similar to those in the examples described withreference to FIGS. 6 and 16, and therefore the description is omitted.

The depth calculation unit 80 calculates, for each pixel or pixel area,the depth-direction distance to the subject 12 taken in the pixel orpixel area, and then obtains the depth distribution of the subject 12 soas to output the obtained depth distribution. The recording unit 58records the depth-distribution information of the subject. The imagecorrection unit 56 performs image correction, such as gray-scalecorrection, for the image data stored in the image memory 54 c so as tooutput the corrected image data as image data of the subject 12. Therecording unit 58 records the image data of the subject 12 together withthe depth-distribution information of the subject 12.

In the above description, the reflected light having the wavelengths λband λc is received by the light-receiving unit 60 b without beingseparated by wavelength from each other. However, in an alternativeexample, the light having the wavelength λb and the light having thewavelength λc may be separated by the separation unit 50 with fourpanels of solid state image sensors serving as the light-receiving unit60. The reflected light beams thus separated are received by differentsolid state capturing devices. In this case, the depth-directiondistance to the subject can be obtained by using the intensities of thereflected light beams respectively having the wavelengths λa, λb and λcin accordance with the same method as that described with reference toFIG. 3.

As described above, according to the image capturing apparatus of thepresent example, the infrared light is used for measuring thedepth-direction of the subject. Thus, even in the conditions where thesubject is also illuminated with natural light or light from lighting,the depth-direction distance of the subject can be measured. Therefore,it is not necessary to keep a room dark in order to measure thedepth-direction distance of the subject. In addition, since the image ofthe subject carried by the reflected light in the visible region can beseparated, the photographic image of the subject can be taken while thedepth distribution of the subject is being measured. Thus, it ispossible to perform an image processing for the subject using the depthdistribution, for example, extraction of a main subject from the takenimage based on the depth distribution or separation of a background andan image of a person.

Although the first and second illumination light beams have theintensity distributions on the optical axes thereof that are differentfrom each other in the above first embodiment, the first and secondillumination light beams may slit light beams each of which extends in avertical direction and may be swept while the intensity of eachillumination light beam is changed along a horizontal direction. In thiscase, a manner of changing the intensity of the first illumination lightbeam is made different from that of the second illumination light beam.If the subject is moving, it is desirable to sweep the first and secondillumination light beams at a considerably high sweeping speed.

Although the optical filter 42 has the first or second transmittancedistribution, the optical filter 42 may have another transmittancedistribution in which the wavelength of the light that can pass throughthe optical filter 42 varies on the incident surface. In this case, theimage capturing apparatus of the present embodiment, the light-receivingunit calculates the depth-direction distance to the subject based on thewavelength of the reflected light received thereby.

Embodiment 2

FIGS. 22A to 22E are diagrams for explaining the principle of the secondembodiment of the present invention. In FIG. 22A, light beams 86 a and86 b are cast onto the subject 12. The light beams 86 a and 86 b haveintensities which decrease along a direction in which the light beams 86a and 86 b travel. The decreasing rate of the intensity of the lightbeam 86 a is the same as that of the light beam 86 b. The light beams 86a and 86 b are reflected by the subject 12, so as to generate reflectedlight beams. When the intensities of the reflected light beams aredetected, the depth-distribution information of the subject 12 from thedetected intensity of the reflected light beams is obtained. In otherwords, when a distant illuminated portion is illuminated with the lightbeams, the intensities of the reflected light beams are weak. On theother hand, when a closer portion is illuminated with the light beams,the intensities of the reflected light beams are stronger. If thereflectance of the subject 12 is pre-known, the distances to theilluminated portions of the subject 12 that are illuminated with thelight beams 86 a and 86 b, respectively, can be calculated from theintensities of the respective reflected light beams, the intensities ofthe light beams 86 a and 86 b when they were emitted, theintensity-modulation rate of the light beam modulated by the modulationunit 82, the reflectance of the subject 12 and the velocity of light.However, it is very hard to measure the reflectance for all possiblesubjects in advance.

Thus, as shown in FIG. 22B, alight beam 88 having an intensity thatdecreases along the traveling direction of the light beam 88 is firstcast on to the subject 12. The light beam 88 is reflected from thesubject 12 to generate a reflected light beam. Then, as shown in FIG.22C, a light beam 92 having an intensity that increases along thetraveling direction of the light beam 92 is cast onto the subject 12.The light beam 92 is also reflected from the subject 12 to generate areflected light beam. Then, the intensities of these reflected lightbeams generated by reflection of the light beams 88 and 92 by thesubject 12 are detected, and the ratio of the intensities is alsocalculated. By calculation of the distance to the subject 12 based onthe reflected-light intensity ratio, adverse effects of the reflectanceof the subject 12 can be canceled.

In the aforementioned method, however, the light beams 88 and 92 arecast onto the subject 12 one by one and the intensity of the reflectedlight beam is performed for each of the light beams 88 and 92. Thus,there arises a time difference between the detection of thereflected-light intensity for the light beam 88 and that for the lightbeam 92, and therefore the aforementioned method cannot be applied to acase where of the subject is moving. In order to overcome this problem,in a method shown in FIG. 22D, the light beams 88 and 92 are providedwith different wavelength characteristics and are cast onto the subject12 simultaneously. Also in this case, the light beam 88 has theintensity that decreases along the traveling direction thereof as shownin FIG. 22B, while the light beam 92 has the intensity that increasesalong the traveling direction thereof as shown in FIG. 22C. The lightbeams 88 and 92 are reflected from the subject 12, as shown in FIG. 22E,so that reflected light beams are generated. The reflected light beamsfrom the subject 12 are separated into wavelength components inaccordance with the wavelengths thereof, and are subjected to thereflected-light intensity detection, thereby the depth-directiondistance of the subject 12 can be measured.

However, since the subject 12 has the difference of the surfacereflectance between the wavelengths, the calculation of thedepth-direction distance may contain an error. In order to reduce thecalculation error, it is necessary to reduce the difference between thewavelengths λ1 and λ2 of the light beams 88 and 92, respectively. On theother hand, when the difference between the wavelengths λ1 and λ2 isreduced, the precision of the separation by the wavelength is alsoreduced, thereby generating the error. Therefore, there arises theaforementioned dilemma and that prevents the improvement of theprecision of the distance measurement.

Accordingly, the first and second illumination light beams are cast onthe subject simultaneously. The first light beam has the firstwavelength characteristics and is modulated in such a manner that theintensity increases along the traveling direction of the first lightbeam, while the second illumination light beam has the second wavelengthcharacteristics different from the first wavelength characteristics andis modulated in such a manner that the intensity decreases along thetraveling direction thereof. Then, the reflected light beam generatedfrom the first illumination light beam and the reflected light beamgenerated from the second illumination light beam are opticallyseparated from each other. Then, the dummy reflected-light intensitythat is expected to be obtained in a case where a light beam having thefirst wavelength characteristics is modulated in such a manner that theintensity decreases along the traveling direction of the firstillumination light beam is calculated by using the reflected light beamgenerated from the second illumination light beam. Finally, thedepth-direction distance to the subject is calculated based on the ratioof the intensity of the reflected light beam generated from the firstillumination light beam to the dummy reflected-light intensity. Byobtaining the dummy reflected-light intensity, the difference of thesurface reflectance between the wavelengths can be cancelled, thus thedepth-direction distance can be precisely obtained. In theaforementioned example, the first illumination light beam has theintensity increasing along the traveling direction thereof while thesecond illumination light beam has the intensity decreasing thetraveling direction thereof. Alternatively, the first illumination lightbeam may have the intensity that decreases along the traveling directionthereof while the second illumination light beam may have the intensitythat increases along the traveling direction thereof. In this case, itis apparent that the dummy reflected-light intensity can be obtained byassuming that a light beam having the first wavelength characteristicshas the intensity that increases along the traveling direction thereof.

FIG. 23 shows an exemplary image capturing apparatus according to thepresent embodiment. The image capturing apparatus of the presentembodiment is the same as those described in the first embodiment exceptthat the illumination unit 40 has a different arrangement; a modulationunit 82 is used for modulating the intensity of the illuminated lightbeam; half mirrors 76 and 78 are used in order to make the optical axisof the illumination unit 40 coincident with that of the capturing unit100; and the depth calculation unit 80 operates in a different manner.As for other components, the same structures as those of thecorresponding components in the first embodiment can be used.

The illumination unit 40 includes a light-source unit 44 and opticalfilters 42 a and 42 b. The optical filter 42 a transmits light havingthe wavelength λa and wavelengths in the vicinity thereof. The opticalfilter 42 b transmits light having the wavelengths λb and λc and thewavelengths in the vicinity thereof. The light-source unit 40 casts thefirst illumination light beam that mainly contains the wavelength λa andhas the intensity varying along the traveling direction thereof and thesecond illumination light beam that mainly contains the wavelengths λband λc and has the intensity varying along the traveling directionthereof, via the optical filter 42 a. The modulation unit 82 modulatesthe intensities of the first and second illumination beams 16 and 18 bytemporal modulation. The wavelengths λa, λb and λc are set to the valuesdescribed in the respective examples of the first embodiment.

The illumination light beams 16 and 18 are reflected by the half mirrors76 and 78 in that order and are directed to the illuminated portion 14of the subject 12. Reflected light beams 22 and 24 generated byreflection of the illumination light beams 16 and 18 by the subject 12pass through the half mirror 78 and are then converged by the opticallens 46 of the capturing unit 100.

Te separation unit 50 separates the reflected light beams into thecomponents of the wavelengths λa, λb and λc. The respective wavelengthcomponents separated by the separation unit 50 are received by thelight-receiving units 60 a, 60 b, and 60 c, respectively. In accordancewith the intensity of the light received by each light-receiving unit60, an electric signal is generated and read into the processing unit110. The separation unit 50 and the light-receiving unit 60 may have thesame structures and functions as those of the separation unit 50, thelight-receiving unit 60 and the processing unit 110 in the respectiveexamples of the first embodiment described with reference to FIGS. 6, 16and 20.

The processing unit 110 has the same structure as that of the processingunit 110 in the respective examples of the first embodiment describedwith reference to FIGS. 7, 17 and 21. A method of calculating the dummyreflected-light intensity in the processing unit 110 is the same orsimilar as/to the calculation method described with reference to FIGS. 8and 18.

FIG. 24 is a flowchart of an exemplary distance measuring method of thepresent embodiment. The illumination unit 40 simultaneously casts thefirst illumination light beam having the wavelength λa and the intensitymodulated along the traveling direction thereof and the secondillumination light beam that has the wavelengths λb and λc that aredifferent from the wavelength λa and the intensity modulated along thetraveling direction thereof. (S300)

The optical lens 46 of the capturing unit 100 converges the reflectedlight beams of the subject 12 (S202). The separation unit 50 opticallyseparates the reflected light beam from the subject 12 so as to separatethe first reflected light beam having the wavelength λa, the secondreflected light beam having the wavelength λb, and the third reflectedlight beam having the wavelength λc (S304).

The light-receiving unit 60 receives the first, second and thirdreflected light beams (S306). The intensity detector 70 of theprocessing unit 110 then detects the intensities Wa, Wb and Wc of thefirst, second and third reflected light beams, respectively (S308).

The depth calculation unit 80 calculates the depth-direction distance tothe subject 12 by using the intensities Wa, Wb and Wc of the first,second and third reflected light beams (S310).

FIG. 25 is a flowchart of an example of the depth-calculation operationS310. First, the dummy reflected-light intensity Wd in a case ofassuming that light having the wavelength λa is modulated in the samemanner as the second illumination light beam, is obtained based on theintensities Wb and Wc of the second and third reflected light beams(S312). The dummy reflected-light intensity Wd can be obtained in thesame manner described in the respective examples of the firstembodiment. Then, the ratio Wa/Wd of the actual intensity Wa of thefirst reflected light beam to the dummy reflected-light intensity Wd(S314) is obtained. Based on the reflected-light intensity ratio Wa/Wdand the intensity-modulation rates of the first and second illuminationlight beams, the depth-direction to the subject is calculated (S316).

FIG. 26 is a flowchart of an example of the distance measuring methodaccording to the present embodiment. In this example, the wavelength λais the middle wavelength between the wavelengths λb and λc.

The illumination unit 40 casts the first illumination light beam havingthe wavelength λa and the intensity modulated along the travelingdirection of the first illumination light beam and the secondillumination light beam having the wavelengths λb and λc onto thesubject 12 simultaneously (S400). The optical lens 46 forms thereflected image of the subject 12 onto which the first and secondillumination light beams are cast (S402). The separation unit 50optically separates the reflected light from the subject 12 into thefirst reflected light beam having the wavelength λa and the secondreflected light beam having the wavelengths λb and λc (S404). Then, aratio Wa/Wd of the intensity Wa of the first reflected light beam to ahalf of the intensity of the second reflected light beam Wd=We/2 (S410).Based on the reflected-light intensity ratio Wa/Wd and theintensity-modulation rates of the first and second illumination lightbeams, the depth of the subject 12 is calculated (S412).

As described above, according to the image capturing apparatus of thepresent invention, illumination light beams having different wavelengthcharacteristics and different intensities are cast onto the subjectsimultaneously. In this case, the reflected light beams from the subjectare subjected to wavelength-separation in accordance with the respectivewavelength characteristics. By using the intensities of the reflectedlight beams thus separated, the depth-direction distance to the subjectcan be obtained simply.

In the present embodiment, since the optical axis of the illuminationlight from the illumination unit and that of the reflected lightincident on the capturing unit are optically the same, there is noregion where the subject illuminated by the illumination unit cannot becaptured by the capturing unit because of shadow. Thus, it is possibleto calculate the depth distribution in the entire region of the subjectilluminated with the illumination light, preventing occurrence of ablind region where the depth-direction distance cannot be calculated.Moreover, by making the optical axes of the illumination unit and thecapturing unit optically the same, the size of the image capturingapparatus can be reduced.

In the present embodiment, the intensity of the illumination light ismodulated by temporal modulation. Thus, it is desirable that thecapturing unit 100 includes a high-speed shutter. The high-speed shuttercaptures an instantaneous value of the intensity of the light receivedby the light-receiving unit 60.

As described above, according to the image capturing apparatus and thedistance measuring method of the present invention, the light beams thathave different wavelength characteristics and have different intensitydistributions on the planes perpendicular to the optical axes thereof orthe intensities modulated in different manners along the travelingdirection thereof are cast onto the subject simultaneously. Then, thereflected light from the subject is optically separated into wavelengthcomponents in accordance with the wavelength characteristics so as tomeasure the intensities, thereby the depth-direction distance to thesubject can be calculated easily and simply.

In the above description, the distance to the subject is obtained basedon the difference of the intensity between the reflected light beams asan example of outgoing light beams from the subject that is illuminatedwith light. However, in a case where the subject is a transparent orsemitransparent object that can transmit the light, the depth of thesubject can be obtained by the difference of the intensity between thetransmitted light beams.

As described above, according to the present invention, the depth of asubject can be easily measured by capturing outgoing light from thesubject illuminated with light.

Although the present invention has been described by way of exemplaryembodiments, it should be understood that many changes and substitutionsmay be made by those skilled in the art without departing from thespirit and the scope of the present invention which is defined only bythe appended claims.

What is claimed is:
 1. An image capturing apparatus for obtaininginformation regarding a depth of a subject, comprising: an illuminationunit operable to cast a first illumination light beam, having a firstwavelength as a main component and a first intensity distribution on aplane perpendicular to an optical axis of said first illumination lightbeam, and a second illumination light beam, having a second wavelengthand a third wavelength as main components and a second intensitydistribution on a plane perpendicular to an optical axis of said secondillumination light beam, onto said subject, said second and thirdwavelengths being different from said first wavelength, said secondintensity distribution being different from said first intensitydistribution; and a depth calculation unit operable to calculate adepth-direction distance to said subject based on outgoing light beamsfrom said subject.
 2. An image capturing apparatus as claimed in claim1, wherein said first illumination light beam has an intensity thatmonotonously increases along a first direction on said planeperpendicular to said optical axis of said first illumination lightbeam, and said second illumination light beam has an intensity thatmonotonously decreases along a second direction on said planeperpendicular to said optical axis of said second illumination lightbeam, said second direction being opposite to said first direction. 3.An image capturing apparatus as claimed in claim 1, wherein said firstillumination light beam has said first intensity distribution in which,with increase of a distance from said optical axis of said firstillumination light beam on said plane perpendicular to said optical axisof said first illumination light beam, an intensity monotonouslyincreases or decreases, and said second illumination light beam has saidsecond intensity distribution in which, with increase of a distance fromsaid optical axis of said second illumination light beam on said planeperpendicular to said optical axis of said second illumination lightbeam, an intensity monotonously decreases when said first illuminationlight beam intensity increases or increases when said first illuminationlight beam intensity decreases.
 4. An image capturing apparatus asclaimed in claim 1, wherein said illumination unit casts said first andsecond illumination light beams onto said subject simultaneously.
 5. Animage capturing apparatus as claimed in claim 4, further comprising: anoptically converging unit operable to converge said outgoing light beamsfrom said subject onto which said first and second illumination lightbeams are cast; a separation unit operable to optically separate saidoutgoing light beams into a first outgoing light beam having said firstwavelength, a second outgoing light beam having said second wavelength,and a third outgoing light beam having said third wavelength; alight-receiving unit operable to receive said first, second and thirdoutgoing light beams after being separated by said separation unit andconverged by said optically converging unit; and a light intensitydetector operable to detect intensities of said first, second and thirdoutgoing light beams received by said light-receiving unit, wherein saiddepth calculation unit calculates said depth-direction distance to saidsubject by the intensities of said first, second and third outgoinglight beams.
 6. An image capturing apparatus as claimed in claim 5,wherein said first illumination light beam has an intensity thatincreases along a first direction on said plane perpendicular to saidoptical axis of said first illumination light beam, said first directionbeing parallel to a line obtained by projecting a line, connecting saidillumination unit to said light-receiving unit or said opticallyconverging unit, on said plane perpendicular to said optical axis ofsaid first illumination light beam, and said second illumination lightbeam has an intensity that increases along a second direction on saidplane perpendicular to said optical axis of said second illuminationlight beam, said second direction being opposite to said firstdirection.
 7. An image capturing apparatus as claimed in claim 5,wherein said illumination unit includes: a first illumination opticalfilter operable to transmit light having said first wavelength, and asecond illumination optical filter operable to transmit light havingsaid second and third wavelengths, said first and second illuminationoptical filters are arranged such that said first and secondillumination light beams are incident on surfaces of said first andsecond illumination optical filters, respectively.
 8. An image capturingapparatus as claimed in claim 7, wherein said first illumination opticalfilter has a transmittance that increases along a first direction on anincident surface thereof, and said second illumination optical filterhas a transmittance that increases along a second direction on anincident surface thereof, said second direction being opposite to saidfirst direction.
 9. An image capturing apparatus as claimed in claim 7,wherein said first illumination optical filter has a transmittance thatincreases or decreases with increase of a distance from said opticalaxis of said first illumination light beam on an incident surfacethereof, and said second illumination optical filter has a transmittancethat, with increase of a distance from said optical axis of said secondillumination light beam on an incident surface thereof, decreases whensaid transmittance of said first illumination optical filter increaseswith said increase of said distance from said optical axis of said firstillumination light beam, or increases when said transmittance of saidfirst illumination optical filter decreases with said increase of saiddistance from said optical axis of said first illumination light beam.10. An image capturing apparatus as claimed in claim 5, wherein saidseparation unit includes: a first outgoing optical filter operable totransmit light having said first wavelength, a second outgoing opticalfilter operable to transmit light having said second wavelength, and athird outgoing optical filter operable to transmit light having saidthird wavelength, said first, second and third outgoing optical filtersare arranged such that said first, second and third outgoing light beamsare incident on said first, second and third outgoing optical filters,respectively.
 11. An image capturing apparatus as claimed in claim 5,wherein said separation unit includes: a first outgoing optical filteroperable to transmit light having said first wavelength, and a secondoutgoing optical filter operable to transmit light having said secondand third wavelengths, said first and second outgoing optical filtersare arranged such that said first outgoing light beam is incident onsaid first outgoing optical filter while said second and third outgoinglight beams are incident on said second outgoing optical filter.
 12. Animage capturing apparatus as claimed in claim 5, wherein saidlight-receiving unit includes a solid state image sensor, and saidseparation unit includes: a first outgoing optical filter that transmitslight having said first wavelength, a second outgoing optical filterthat transmits light having said second wavelength, and a third outgoingoptical filter that transmits light having said third wavelength, saidfirst, second and third outgoing optical filters being arrangedalternately on a light-receiving surface of said solid state imagesensor.
 13. An image capturing apparatus as claimed in claim 5, whereinsaid depth calculation unit calculates said depth-direction distance tosaid subject by the intensity of said first outgoing light beam and avalue based on the intensities of said second and third outgoing lightbeams.
 14. An image capturing apparatus as claimed in claim 13, whereinsaid depth calculation unit calculates said depth-direction distance tosaid subject by the intensity of said first outgoing light beam and anaveraged intensity of the intensities of said second and third outgoinglight beams.
 15. An image capturing apparatus as claimed in claim 4,wherein said second wavelength is shorter than said first wavelengthwhile said third wavelength is longer than said first wavelength, andsaid image capturing apparatus further comprising: an opticallyconverging unit operable to converge said outgoing light beams from saidsubject onto which said first and second illumination light beams arecast; a separation unit operable to optically separate said outgoinglight beams into a first outgoing light beam having said firstwavelength and a second outgoing light beam having said second and thirdwavelengths; a light-receiving unit operable to receive said first andsecond outgoing light beams after being separated by said separationunit and converged by said optically converging unit; and a lightintensity detector operable to detect intensities of said first andsecond outgoing light beams received by said light-receiving unit,wherein said depth calculation unit calculates said depth-directiondistance to said subject by the intensities of said first and secondoutgoing light beams.
 16. An image capturing apparatus as claimed inclaim 15, wherein said depth calculation unit calculates saiddepth-direction distance to said subject by the intensity of said firstoutgoing light beam and one half of the intensity of said secondoutgoing light beam.
 17. An image capturing apparatus as claimed inclaim 16, wherein said light intensity detector calculates theintensities of said first and second outgoing light beams for each pixelof an image of said subject taken by said light-receiving unit, and saiddepth calculation unit calculates a depth distribution of said subjectby obtaining said depth-direction distance to a region of said subjectcorresponding to every pixel of said image.
 18. An image capturingapparatus as claimed in claim 17, wherein said first and secondillumination light beams are light beams in an infrared region, saidseparation unit further includes: a device operable to opticallyseparate visible light from said outgoing light beams from said subject,said light-receiving unit further includes: a solid state image sensorfor visible light operable to receive said visible light that isoptically separated by said separation unit and is converged by saidoptically converging unit, and said image capturing apparatus furthercomprises: a recording unit operable to record both said depthdistribution of said subject calculated by said depth calculation unitand said image of said subject taken by said solid-state image sensorfor visible light.
 19. An image capturing apparatus as claimed in claim15, wherein said light intensity detector calculates the intensities ofsaid first and second outgoing light beams for each pixel of an image ofsaid subject taken by said light-receiving unit, and said depthcalculation unit calculates a depth distribution of said subject byobtaining said depth-direction distance to a region of said subjectcorresponding to every pixel.
 20. An image capturing apparatus asclaimed in claim 19, wherein said first and second illumination lightbeams are light beams in an infrared region, said separation unitfurther includes: a device operable to optically separate visible lightfrom said outgoing light beams from said subject, said light-receivingunit further includes: a solid state image sensor for visible lightoperable to receive said visible light that is optically separated bysaid separation unit and is converged by said optically converging unit,and said image capturing apparatus further comprises: a recording unitoperable to record both said depth distribution of said subjectcalculated by said depth calculation unit and said image of said subjecttaken by said solid-state image sensor for visible light.
 21. A distancemeasuring method for obtaining information regarding a depth of asubject, comprising: an illumination step for simultaneously casting afirst illumination light beam, having a first wavelength as a maincomponent and a first intensity distribution on a plane perpendicular toan optical axis of said first illumination light beam, and a secondillumination light beam, having a second wavelength and a thirdwavelength as main components and a second intensity distribution on aplane perpendicular to an optical axis of said second illumination lightbeam, onto said subject, said second and third wavelengths beingdifferent from said first wavelength, said second intensity distributionbeing different from said first intensity distribution; a separationstep for optically separating outgoing light beams from said subjectonto which said first and second illumination light beams are cast intoa first outgoing light beam having said first wavelength, a secondoutgoing light beam having said second wavelength, and a third outgoinglight beam having said third wavelength; a capturing step for capturingsaid first, second and third outgoing light beams; a light intensitydetection step for detecting intensities of said captured first, secondand third outgoing light beams; and a depth calculation step forcalculating a depth-direction distance to said subject based on saidintensities of said first, second and third outgoing light beams.
 22. Adistance measuring method as claimed in claim 21, wherein said depthcalculation step includes calculating said depth-direction distance tosaid subject based on said intensity of said first outgoing light beamand a value based on said intensities of said second and third outgoinglight beams.
 23. A distance measuring method as claimed in claim 21,wherein said depth calculation step includes calculating saiddepth-direction distance to said subject based on said intensity of saidfirst outgoing light beam and an averaged intensity of said intensitiesof said second and third outgoing light beams.
 24. A distance measuringmethod for obtaining information regarding a depth of a subject,comprising: an illumination step for simultaneously casting a firstillumination light beam, having a first wavelength as a main componentand a first intensity distribution on a plane perpendicular to anoptical axis of said first illumination light beam, and a secondillumination light beam, having a second wavelength and a thirdwavelength as main components and a second intensity distribution on aplane perpendicular to an optical axis of said second illumination lightbeam, onto said subject, said second wavelength being shorter than saidfirst wavelength, said third wavelength being longer than said firstwavelength, said second intensity distribution being different from saidfirst intensity distribution; a separation step for optically separatingsaid outgoing light beams into a first outgoing light beam having saidfirst wavelength and a second outgoing light beam having said second andthird wavelengths; a capturing step for capturing said first and secondoutgoing light beams; a light intensity detection step for detectingintensities of said first and second outgoing light beams; and a depthcalculation step for calculating a depth-direction distance to saidsubject based on said intensities of said first and second outgoinglight beams.
 25. A distance measuring method as claimed in claim 24,wherein said depth calculation step includes calculating saiddepth-direction distance to said subject based on said intensity of saidfirst outgoing light beam and one half of said intensity of said secondoutgoing light beam.